追踪复杂造山带的流体特征和金属流动性:比利牛斯轴心区铅锌矿化的启示

IF 4.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Alexandre Cugerone, Stefano Salvi, Kalin Kouzmanov, Oscar Laurent, Bénédicte Cenki
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引用次数: 0

摘要

造山过程包括变形和变质事件的复杂相互作用,会对矿床的形成产生不同程度的影响。然而,由于缺乏在多次成矿后再加工过程中不受影响的可靠地球化学指标,区分造山过程与成矿后过程的流体特征是一项重大挑战。本研究仔细研究了原生和次生流体包裹体(FIs)的性质和化学性质,确定了与南法国/北伊比利亚比利牛斯轴带(PAZ)不同风格的铅锌矿化有关的两种流体群的不同特征:其中包括晚石炭纪地层表生铅锌矿床和中生代横切铅锌(-Ge)矿脉系统。在一些横切铅锌矿脉中的原生和次生FIs中发现了种群(I),它是地层表生体中的次要成分。它表现出以 Na 为主的中低盐度(< 20 wt% NaCl 当量)、中等温度(200-350 °C)、大量富含 CO2 的 FIs,并显示出较低的同质 Cl/Br 摩尔比。这些特征与流体的变质起源一致,与晚期瓦利斯坎变质作用有关。(II)类群通常出现在横切矿脉系统中,作为原生和假次生FIs出现,也出现在地层表生体中,是次生FIs的主要流体成分。种群(II)以钙为主,具有中高盐度(15-35 wt% NaCl当量),温度相对较低(< 200 °C),Cl/Br摩尔比很高,但变化很大。最后一个特征是至少两种流体混合的典型特征,一种流体在地壳浅层可能具有较低的 Cl/Br 摩尔比,另一种流体在地壳深层具有较高的 Cl/Br 摩尔比。群(II)的特征与中生代期间在比利牛斯山脉循环时与基底相互作用的基底流体相一致,但不能排除比利牛斯-阿尔卑斯时代的流体。我们发现,在横切矿脉中形成迹线的闪锌矿寄生次生燧石中,有证据表明存在高浓度的 Ge(高达几千 ppm),这与异常的 Pb 和 Tl 浓度相关。在主要位于深层高品位变质岩中的矿脉中发现了极高的金属浓度(铅、锌含量高达 1-2 wt%),这与 Cl/Br 摩尔比成反比。根据文献中的流体数据汇编,可以推断出矿化所处岩石的变质品位与 FIs 中铅和锌含量之间的一阶相关性。早期的地层矿体被认为是后期横切脉矿化发展的可能金属来源。这项研究证明了造山带流体循环的重要性和复杂性,并支持地壳中预先存在的金属富集的重要性,特别是高品位变质岩中的金属富集是在复杂的多期造山带中形成铅锌矿脉的先决条件。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Tracing fluid signature and metal mobility in complex orogens: insights from Pb-Zn mineralization in the Pyrenean Axial Zone

Tracing fluid signature and metal mobility in complex orogens: insights from Pb-Zn mineralization in the Pyrenean Axial Zone

Orogenic processes encompass a complex interplay of deformation and metamorphic events, which can impact the formation of ore deposits to various degrees. However, distinguishing fluid signatures from orogenic versus post-orogenic events presents a significant challenge due to the scarcity of robust geochemical indicators that remain unaffected during multiple post-mineral reworking events. This study carefully examines the properties and chemistry of primary and secondary fluid inclusions (FIs), identifying distinct signatures of two fluid populations linked to different styles of Pb-Zn mineralization in the Pyrenean Axial Zone (PAZ) of Southern-France/Northern-Iberia: These included late-Carboniferous stratabound epigenetic Pb-Zn deposits and Mesozoic crosscutting Pb-Zn(-Ge) vein systems. Population (I) is identified in primary and secondary FIs in a few crosscutting Pb-Zn veins and constitutes a minor component in stratabound epigenetic bodies. It exhibits Na-dominated low to intermediate salinity (< 20 wt% NaCl eq.), intermediate temperatures (200–350 °C), abundant CO2-rich FIs and shows low homogeneous Cl/Br molar ratios. These characteristics are consistent with a metamorphic origin of the fluids, associated with Late-Variscan metamorphism. Population (II) is commonly observed in the crosscutting vein systems where it occurs as primary and pseudosecondary FIs, as well as in stratabound epigenetic bodies where it represents the main fluid component of secondary FIs. Population (II) is Ca-dominated with intermediate to high salinity (15–35 wt% NaCl eq.), relatively low temperature (< 200 °C), and shows high Cl/Br molar ratios with significant variations. This last characteristic is typical of mixing of at least two fluids, one with a probable low Cl/Br molar ratio at shallow crustal levels and another with high Cl/Br molar ratio at deeper levels. Characteristics of population (II) are consistent with a fluid of basinal origin that interacted with the basement while circulating in the Pyrenees during the Mesozoic, although a Pyrenean-Alpine age cannot be excluded. Locally, in sphalerite-hosted secondary FIs that form trails in the crosscutting veins, we find evidence of high Ge concentrations (up to few 1000s ppm), which correlate with anomalous Pb and Tl concentrations. Very high metal concentrations (up to 1–2 wt% Pb, Zn), which are inversely proportional to Cl/Br molar ratios, are found in FIs mainly within veins hosted in deep-seated high-grade metamorphic rocks. Based on a compilation of fluid data from the literature, a first-order correlation can be deduced between the metamorphic grade of the rocks hosting the mineralization and the Pb and Zn content in the FIs. Early stratabound orebodies are considered likely sources of metal for the development of the late crosscutting vein mineralization. This study demonstrates the significance and complexity of orogen-scale fluid circulation and supports the importance of pre-existing metal enrichment in the crust, especially in high-grade metamorphic rocks as a prerequisite for the formation of Pb-Zn veins in complex multi-stage orogens.

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来源期刊
Mineralium Deposita
Mineralium Deposita 地学-地球化学与地球物理
CiteScore
11.00
自引率
6.20%
发文量
61
审稿时长
6 months
期刊介绍: The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.
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